NO removal performance of CO in carbonation stage of calcium looping for CO2 capture

Abstract

Calcium looping realizes CO 2 capture via the cyclic calcination/carbonation of CaO. The combustion of fuel supplies energy for the calciner. It is unavoidable that some unburned char in the calciner flows into the carbonator, generating CO due to the hypoxic atmosphere in the carbonator. CO can reduce NO in the flue gases from coal-fired power plants. In this work, NO removal performance of CO in the carbonation stage of calcium looping for CO 2 capture was investigated in a bubbling fluidized bed reactor. The effects of carbonation temperature, CO concentration, CO 2 capture, type of CaO, number of CO 2 capture cycles and presence of char on NO removal by CO in carbonation stage of calcium looping were discussed. CaO possesses an efficient catalytic effect on NO removal by CO. High temperature and high CO concentration lead to high NO removal efficiency of CO in the presence of CaO. Taking account of better NO removal and CO 2 capture, the optimal carbonation temperature is 650 °C. The carbonation of CaO reduces the catalytic activity of CaO for NO removal by CO due to the formation of CaCO 3 . Besides, the catalytic performance of CaO on NO removal by CO gradually decreases with the number of CO 2 capture cycles. This is because the sintering of CaO leads to the fusion of CaO grains and blockage of pores in CaO, hindering the diffusion of NO and CO. The high CaO content and porous structure of calcium-based sorbents are beneficial for NO removal by CO. The presence of char promotes NO removal by CO in the carbonator. CO 2 /NO removal efficiencies can reach above 90%. The efficient simultaneous NO and CO 2 removal by CO and CaO in the carbonation step of the calcium looping seems promising.